Seven-Second Subnetting Process

Introduction

• Previous videos covered converting IP addresses and subnet masks to binary, performing calculations, and converting back to decimal.
• Introduced the magic number method for quicker subnetting calculations.
• The seven-second subnetting shortcut avoids binary-decimal conversions and simplifies subnetting.

Key Concepts

• Magic Number Method: Previously explored shortcut with calculations.
• Seven-Second Subnetting: No math needed, uses a predefined chart.
• Subnetting Purpose: Splitting a network into smaller subnets.
  • Example: 256 hosts into subnets of 128, 64, etc.

Creating the Subnetting Chart

• Chart Components:
  • Subnet masks (CIDR to decimal conversion)
  • Networks column: Start with 2, double till 256.
  • Addresses column: Start with 128, divide by 2 till 1.
  • Decimal subnet mask column for easy reference.
• Benefits: Allows quick calculations without additional math.

Subnetting Process

1. Convert IP Address and Subnet Mask to Decimal:
   • Use chart for CIDR block to decimal conversion.
2. Determine Subnet Address:
   • Refer to chart for subnet boundaries.
3. Calculate Broadcast Address:
   • Identify last address in subnet range.
4. Calculate Usable IP Addresses:
   • First IP: Subnet address + 1.
   • Last IP: Broadcast address - 1.

Examples

• Example 1: IP 165.245.12.88/24

  • Subnet mask: 255.255.255.0
  • Network address: 165.245.12.0
  • Broadcast address: 165.245.12.255
  • First IP: 165.245.12.1
  • Last IP: 165.245.12.254

• Example 2: IP 165.245.12.88/26

  • Subnet mask: 255.255.255.192
  • Network address: 165.245.12.64
  • Broadcast address: 165.245.12.127
  • First IP: 165.245.12.65
  • Last IP: 165.245.12.126

• Example 3: IP 165.245.12.88/20

  • Subnet mask: 255.240.0.0
  • Network address: 165.240.0.0
  • Broadcast address: 165.255.255.255
  • First IP: 165.240.0.1
  • Last IP: 165.255.255.254

• Example 4: IP 18.172.200.77/11

  • Subnet mask: 255.224.0.0
  • Network address: 18.160.0.0
  • Broadcast address: 18.191.255.255
  • First IP: 18.160.0.1
  • Last IP: 18.191.255.254

• Example 5: IP 18.172.200.77/17

  • Subnet mask: 255.255.128.0
  • Network address: 18.172.128.0
  • Broadcast address: 18.172.255.255
  • First IP: 18.172.128.1
  • Last IP: 18.172.255.254

Exam Tips

• Write or type the chart quickly for reference.
• Consider bringing a fine-tip dry erase pen to testing centers.
• Choose a subnetting shortcut that works best for you.